The principal goal of this project is to elucidate the mechanisms of the sodium, potassium pump (Na,K-ATPase) and the calcium pump (SERCA ATPase). In particular we are interested in explaining the transient kinetics of these pumps. A collaboration with J. Froehlich of NIA is directed at determining the extent to which our transient kinetic observations restult from oligomeric interactions of the catalytic subunits of these pumps. One hypothesis is that they contribute to the efficiency of cation transport. Our evidence suggests that "out-of-phase" interactions of two or more alpha subunits occur in the native state of these P-type cation pumps. We have begun additional collaborations to permit further tests of these hypotheses.